1. EQ: How do different mediums affect the speed of sound?

2. What are the characteristics of sound waves?
Properties of Sound
What are the characteristics of sound waves?

3. Properties of Sound
sound wave: a longitudinal wave that is caused by vibrations and that travels through a material medium

4. In air, sound waves spread out in all directions away from the source.
Properties of Sound
In air, sound waves spread out in all directions away from the source.

5. 16-1-3 Properties of Sound, continued
Sound waves travel faster through liquids and solids than through gases because the greater the density of the medium the better the transmission.

6. Properties of Sound, continued
Speed of Sound in Various Mediums
Table 1, p.491

7. 16-1-4 Properties of Sound, continued
loudness: is the effect that intensity has on the ear

8. 16-1-5 Properties of Sound, continued
intensity: depends on amplitude and distance and describes the rate at which a sound wave transmits energy through a given area of a medium

9. 16-1-6 Properties of Sound, continued
Intensity is measured in units called decibels, dB.

10. 16-1-7 Properties of Sound, continued
pitch: is the ear’s perception of frequency

11. 16-1-8 Properties of Sound, continued
infrasound: frequencies lower than 20 Hz which are below the range of human hearing

12. 16-1-9 Properties of Sound, continued
ultrasound: frequencies higher than 20,000 Hz which are above human hearing range

13. 16-1-10 Musical Instruments
How do musical instruments make sound?

14. 16-1-10 Musical Instruments
Most instruments rely of standing waves produced through the vibration of strings, air columns, or membranes.

15. 16-1-11 Musical Instruments
Standing waves can exist only at certain wavelengths on a string.

16. 16-1-12 Musical Instruments
fundamental frequency: The primary standing wave on a vibrating string has a wavelength that is twice the length of the string.

17. 16-1-13 Musical Instruments, continued
Resonance: a phenomenon that amplifies sound
when two objects naturally vibrate at the same frequency

18. 16-1-14 Musical Instruments, continued
natural frequencies: the specific frequencies at which an object is most likely to vibrate depending on the object’s shape, size, mass, and the material from which the object is made.

19. How do ears help humans hear sound waves?
Hearing and the Ear
How do ears help humans hear sound waves?

20. Hearing and the Ear
The human ear is divided into three regions—outer, middle, and inner in which vibrations in the air are sensed, amplified, and transmitted to the brain.

21. 16-1-17 Hearing and the Ear, continued
Hair cells near the part of the membrane that vibrates then stimulate nerve fibers that send an impulse to the brain.

22. Ultrasound and Sonar How are the reflections of sound waves used?
Reflected sound waves are used to determine distances and to create images.
Some ultrasound waves are reflected at boundaries.

23. Ultrasound and Sonar, continued
Ultrasound imaging is used in medicine.
The echoes of very high frequency ultrasound waves, between 1 million and 15 million Hz, are used to produce computerized images called sonograms.
Some ultrasound waves are reflected at boundaries.
Some sound waves are reflected when they pass from one type of material into another.
How much sound is reflected depends on the density of the materials at each boundary.
The reflected waves can be made into a computer image called a sonogram.

24. Ultrasound and Sonar, continued
Sonar is used to locate objects underwater.
Sonar: sound navigation and ranging, a system that uses acoustic signals and echo returns to determine the location of objects or to communicate
A sonar system determines distance by measuring the time it takes for sound waves to be reflected back from a surface.
d = vt
d is distance
v is the average speed of the sound waves in water
t is time